How to model a Coral or Sponge Structure?
I'm not sure you can get anything good with a bump map or procedurally, especially if you're supposed to make a "perfect copy", so I guess you'll have to make the mesh manually: create a cylinder, mirror it, use your picture as background to follow the shape, cut the holes profiles with the knife, extrude, add some edges with the knife to make a nice topology with quads, etc.